In general, soybean which is one of the pulse crops contains isoflavone compounds including daidzin, daidzein, genistin and genistein.
The isoflavone compounds are represented by the following formula and Denotative Table. ##STR1##
______________________________________ Denotative Table R1 R2 ______________________________________ daidzin H glucose daidzein H H genistin OH glucose genistein OH H ______________________________________
Of these isoflavone compounds, daidzein is an aglycone of daidzin having its glucose as a glycosidic saccharide hydrolytically separated therefrom, and genistein ia an aglycone of genistin having its glucose as a glycosidic saccharide hydrolytically separated therefrom. With respect to the isoflavone compounds, contents thereof and percentages between daidzin and daidzein and between genistin and genistein in a defatted soybean are shown in the following Table 1.
TABLE 1 ______________________________________ daidzin daidzein genistin genistein ______________________________________ defatted soybean 100 3.2 180 4.2 (96.9%) (3.1%) (97.7%) (2.3%) ______________________________________ (unit: mg/100 g)
It is understood from Table 1 that, in soybean, daidzin and genistin are contained in large amounts while daidzein and genistein which are aglycones thereof are contained in smaller amounts.
On the other hand, it has been reported that a glycosidic saccharide is hydrolyzed from an isoflavone compound contained in soybean to form an aglycone in the course of soy sauce or miso (fermented soybean paste) preparation [see Kihara, K.: Journal of Japan Soy Sauce Research Institute (for SHO-KEN), 16, 5, 190(1990)].
According to this report, although hydrolysis of a glycosidic saccharide proceeds to some extent by cooking of a defatted soybean or in a koji preparation step (seigiku step), most of the saccharide has already hydrolytically been separated in soy sauce cake or a soybean miso. However, since these are highly salinized, it should be avoided to ingest these in large amounts. Accordingly, it is difficult to employ any of processes for preparing these as a process for preparing a food from a pulse crop as a starting material.
In soybeans soyasaponins occur. For example, in a defatted soybeans soyasaponins occur in an amount of 500 to 700 mg/100 g. It has been reported that soyasaponins consist of 5 varieties of saponins, i. e., soya saponin I, soya saponin II, soya saponin III, soya saponin A1 and soya saponin A2 in the form of a mixture [see Kitagawa et al.: YAKUGAKU ZASSHI, 104, 2, 162-168(1984)]. Each of these has glucuronic acid as a glycosidic saccharides and the aglycone which is such a compound that the glycosidic saccharide is removed therefrom includes two varieties of soyasapogenol A and soyasapogenol B. In general, however, the aglycone is present as soyasapogenol B. In a commercially available soybean miso, however, neither soyasapogenol A nor soyasapogenol B was detected.
Further, many reports have been made on pharmacological activities of various constituents contained in pulse crops.
For example, a Pueraria lobata OHWI (kudzu) which is one of legume has been used for a long time as a material for an infusion of Pueraria root (Puerariae Radix) as a herb medicine. It has been reported that isoflavone compounds and saponins contained in pueraria root have liver function improving activities (therapeutic activities against hepatopathy) [see "Nohara et al.: Journal of Medical and Pharmaceutical Society (for WAKAN-YAKU), 5, 408-409(1988", "Y. Niiho etal.: YAKUGAKU ZASSHI, 109, 6, 424-431(1989)" and "Y. Niiho et al.: YAKUGAKU ZASSHI, 110, 8, 601-611(1990)"]. Specifically, an alcohol concentration, an acetaldehyde concentration and an concentration of ketones in blood can be lowered to prevent hangover, nasty aftereffects of drink or the like, and metabolic dysfunction of liver can be prevented. Further, it has been reported that soyasaponins contained in soybean have anti-inflammatory activity, and activities of reducing serum cholesterol, neutral fat and phospholipid (cardiac function improving activity, lipotropic activity, antidiabetic activity, antifat activity, flesh reducing activity) as well as the above-mentioned activity in common with pueraria root [see Ohminami et al.: EIYO TO SHOKURYO, 34, 2, 105-108(1981)].
It is said that although soyasaponins have the activities of improving functions of a living body as described above, soyasaponins in the form of a glycoside as such can not be absorbed in a body. Accordingly, saponins in the form of a glycoside are not intestinally absorbable until it is decomposed into its aglycone, i.e., soyasapogenol B by enterobacteria having .beta.-glucuronidase activity. It is said that the decomposition takes a lot of time and thus there the aglycone has a little chance of being absorbed by a small intestine to lead to an extremely low absorption efficiency. On the other hand, the enterobacteria having .beta.-glucuronidase activity is not regarded as useful enterobacteria. Accordingly, placing no reliance on the decomposition by the enterobacteria, it is desired that soyasaponins be preliminarily decomposed in vitro into soyasapogenol B to ingest the latter. The same desire is true of the soy isoflavone compounds.
Further, soyasapogenol B is a triterpene compound and effective as an endotherine (ET) converter enzyme inhibitor (see Japanese Patent Laying-Open Publication No.188033/1995) and inhibits an endotherine converter enzyme from exhibiting its function, and hence soyasapogenol B is effective as a remedy for endotherine (ET)-related disorders such as hypertension, cerebrovascular contraction after subarachnoid hemorrhage, myocardial infarction, arteriosclerosis, heart failure, renal failure, asthma, and so forth. Further, the triterpene compound has lipase inhibitory activity and glycerophosphate dehydrogenase inhibitory activity. Accordingly, the triterpene compound is capable of inhibiting decomposition of lipids to prevent the lipids from being absorbed in a body, and thus, it is effective for prevention and treatment of fatness (see Japanese Patent Laying-Open Publication No.40689/1997, and Japanese Patent Laying-Open Publication No.67249/1997) and expected to exhibit cardial function improving activity and flesh reducing activity. Therefore, it is desired that soyasaponins be decomposed to obtain soyasapogenol B as an aglycone of saponins.
Moreover, it has been reported that free myo-inositol and the like which are formed by decomposition of phytic acid in contents of soybean have liver function improving activities of facilitating lipometabolism in a liver (therapeutic activities against hepatopathy) (see Kubota, H.: FOOD CHEMICAL, 8, 83-89 (1987).
Further description will be made on the promotion of liver function. It has been reported that miso soup has anti-cancer effect, and this is because enzyme activity of a liver is enhanced by ingestion of miso soup [see Kanke, S.: SHOKU NO KAGAKU, 224, 50-54(1996)]. Specifically, it is reported that when iron as a carcinogen and oxidant and miso are fed to a rat or mouse, activity of glutathione-s-transferase (GST) is increased. GST has been known to combine a carcinogen with glutathione to form a glutathione conjugate, which is excrete from a body. It is said that phase II xenobiotic-metabolizing enzymes to enhance carcinogen detoxication and elimination such as NAD(P)H: quinone oxidoreductase (DT diaphorase) and aldehyde dehydrogenase, as well as conjugating enzymes such as GST and UDP-glucuronosyl-transferase.
Accordingly, many proposals concerning isoflavone compounds contained in soybean have been made in Japanese Patent Laying-Open Publication No.126186/1987, Japanese Patent Laying-Open Publication No.258669/1989, Japanese Patent Laying-Open Publication No.170756/1993, and so on.